Conventionally, to main circuit connection of transformer station and electric power-applied section of high-voltage cable, a thermo-sensing label is attached such that its color changes to indicate that a state of exceeding a predetermined temperature continues for a certain period for the purpose of constantly supplying electric power, thereby allowing the maintenance worker to visually monitor it.
FIGS. 1(a) to (c) show a conventional structure for supporting the transmission line at a power transmission tower. FIG. 1(a) shows a schematic composition of the power transmission tower. FIG. 1(b) shows a support portion for the transmission line. The power transmission tower 2 is composed of cable supporting portions 2A to support the transmission lines 3A, 3B and 3C, and insulators 8 that are connected to the top of the cable supporting portions 2A to suspend the transmission lines 3A, 3B and 3C while insulating from the lines. The cable clamp 7 attached to each of the transmission lines 3A, 3B and 3C is fixed to the insulator 8 to support each of the transmission lines 3A, 3B and 3C. The thermo-sensing label is attached on the surface of the cable clamp 7.
FIG. (c) shows the thermo-sensing label 10, which includes a temperature indicating section 10A that is of a thermo-sensitive material whose color changes according to temperature, and temperature index sections 10B (red[higher than 65° C.]) and 10C (yellow[higher than 50° C.]) that indicate the relation of color indicated by the temperature indicating section 10A and the temperature. The temperature indicating section 10A has irreversibility that the state of having the color once changed is retained. For example, when the temperature of cable clamp 7 is kept higher than 65° C. for a certain time due to electrical overload, its color changes to red and after that the color changing state is retained. Therefore, when it is found in the maintenance check that the thermo-sensing label 10 has the color changed, it can be visually and easily checked that the cable clamp 7 reached a high temperature. An increase in temperature of the cable clamp 7 can be caused by loosing of a bolt, deterioration of a cable, increasing of load due to an increase in amount of current carried.
Japanese patent application laid-open No.5-66714 discloses a thermo-sensing label that has a temperature indicating section of a thermo-sensitive material with reversibility. In the thermo-sensing label, the transparency of the thermo-sensitive material varies between transparent and white opaque depending on temperature, and the thermo-sensitive material has reversibility in transparency. Therefore, the thermo-sensing label can be used repeatedly.
However, in the conventional temperature monitoring system using the thermo-sensing label, there is a problem that even when a periodical temperature change not reaching the extraordinary temperature occurs at the electric power-applied section due to an increase in amount of current carried, it cannot be detected since the system is designed to detect that its-monitored object reaches an extraordinary temperature.
Also, in the conventional temperature monitoring system, it is necessary to visually check the color change of temperature indicating section. Therefore, in such a place that cannot be easily accessed by the maintenance worker for safety reasons, the object to be monitored will be subject to limitations. When remote monitoring by a camera etc. is employed instead of visually checking, it will be costly.
It is an object of the invention to provide a temperature monitoring system for electric power-applied section that can safely and at low cost monitor a temperature change of electric power-applied section without having a monitored object limited and obtain a temperature history record according to a situation of monitored object.